It may be desirable in many instances to stretch a web in the cross-web direction during processing. For example, webs including layers of inelastic materials, e.g., nonwoven webs, laminated or otherwise attached to elastic layers typically require stretching to impart elasticity to the web. Stretching the web such that inelastic layers or bonds within the inelastic layer or layers are broken or otherwise disrupted leaves the stretched web elastic due to the one or more layers of elastic materials located within the web. Such stretching to impart elasticity to a web is commonly referred to as “activation” of the web (with the elasticity of the web being “activated” by the stretching). Activation can be performed by a variety of methods including, for example, tentering and ring rolling.
Tentering typically involves grasping the edges of a web and stretching the web in the cross-web direction while advancing the web in the down-web direction (i.e., along the length of the web). Although tentering does provide the ability to vary the amount of strain induced in the web, it also suffers from a number of disadvantages. For example, the edges of the web must often be discarded after tentering due to damage or inconsistent strain in the web at the edges. Another potential disadvantage is that it may be difficult or impossible to induce strain into selected portions or zones of a web using tentering. Further, tentering equipment can be both costly, complex, and may require significant amounts of floorspace to operate.
Ring rolling does offer an alternative to tentering for stretching a web. Various ring rolling apparatus are described in, e.g., U.S. Pat. No. 5,143,679 (Weber et al.); U.S. Pat. No. 5,156,793 (Buell et al.); and U.S. Pat. No. 5,167,897 (Weber). Although ring rolling can be used to stretch selected zones in a web, disadvantages of ring rolling may include, for example, contact of the web by the ring rolling apparatus that may undesirably affect the web's appearance. The amount of strain that can be induced in a web using ring rolling may be limited by the ring rolling equipment. Adjustment or change in the stretch amounts may be difficult or limited. Further, the ring rolling equipment typically must be stopped to effect changes in the amount of stretch. In addition, ring rolling typically involves the rapid application of non-linear strain to the web, such that the web may tear or rupture, thereby resulting in excessive waste.